The invention relates to precision coils, and more particularly to precision control methods for producing precision coils.
High intensity, highly uniform magnetic fields are required for successful magnetic resonance imaging (MRI). The high intensity magnetic fields may be achieved using superconducting coils and cryogenic cooling. In some instances, to promote thermal and mechanical stability of such superconducting coils, it is desirable to support the wire within a layer of epoxy. The manufacture of these superconducting coils is subject to a high cost of superconducting wire and the relative difficulty of achieving consistency and uniformity in the distribution of the epoxy throughout the coil pack. Due to stringent electromagnetic requirements, and high thermal and mechanical stresses that pose a risk of magnet quench, it is desirable for these magnetic resonance (MR) coils to be free of defects such as gaps, ride-ups, drop-ins, and other anomalies. These cost and quality requirements constrain the manufacturing process to include precise control over the winding geometry, wherein it is desirable to form coils that consist of densely packed wire wound free of defects, while maintaining a precise layer by layer turn count.
Existing coil winding methods employ a winding machine in which the wire, maintained at constant tension, traverses linearly in a direction parallel to the axis of rotation of a spindle. In high precision applications involving small wire diameters and large coil diameters, absent the required degree of automatic control, operators may need to provide small-scale steering adjustments along with error detection and correction. However, manual correction is susceptible to human errors. Additionally, manual correction slows the process of coil winding.
Moreover, it may be noted that epoxy-supported coils are especially difficult to manufacture with precision. For example, the turns of a coil impregnated with epoxy may be difficult to place at the desired location, as the turns may slip from the desired location due to presence of the epoxy. Wet winding methods, in which the wire is coated with epoxy along the path to the winding bobbin, as opposed to being coated after winding, may be employed to maximize coverage of the epoxy. As will be appreciated, it is desirable to dispose the exact number of turns into the available space between the flanges of a winding bobbin and the correct nesting of wire between layers. Any substantial deviation of wire placement may accumulate during the winding process, and result in either insufficient space to place the desired number of turns, or extra space between turns, causing the next layer in the same location to ride up or drop in, respectively.